1. Field of the Invention
The present invention relates to a computer program product, system, and method for facilitating read operations in a volume.
2. Description of the Related Art
In certain computing environments, multiple host systems may configure data sets in volumes configured in a storage system, such as interconnected storage devices, e.g., a Direct Access Storage Device (DASD), Redundant Array of Independent Disks (RAID), Just a Bunch of Disks (JBOD), etc. Data sets are comprised of extents, which may comprise any grouping of tracks and data storage units. The Z/OS® operating system from International Business Machines Corporation (“IBM”) has a Volume Table of Contents (VTOC) to provide information on data sets of extents configured in the volume, where the VTOC indicates the location of tracks, extents, and data sets for a volume in storage.
To avoid loss of data, data stored on a volume (often referred to as a primary volume) may be backed up by copying it to another volume (often referred to a secondary volume) frequently stored at another geographical location. Accordingly, in the event that data on the primary volume is lost due to data corruption, hardware or software failure, or a disaster which destroys or damages the primary volume, the backup data may be retrieved from the secondary volume.
To preserve the backup data on the secondary volume until it is needed, in some environments, both read and write operations directed to the secondary volume may be disabled. For example, in some operating systems, a read operation directed to a volume causes the operating system to generate an associated write operation as well. For example, if a particular data set is to be read, a “last referenced date” field of the VTOC may updated by the operating system to indicate when that data set was last accessed. Accordingly, if write operations for a secondary volume are disabled to preserve the integrity of the data stored on the secondary volume, a read operation will frequently fail as well since the read operation causes the operating system to attempt to write data to the secondary volume. As a result, read operations are frequently disabled as well as write operations, to prevent all attempts to change the data stored on the secondary volume. Thus, applications which seek to perform read operations only may also be prevented from accessing the data stored on the secondary volume.
One approach to permitting read operations is to create an unmodified clone of the original file if the file is modified. The modified file and the unmodified clone may be stored separately. Another approach is use a database to keep track of modified file versions.